Sirius was raised in The House Of Black, which means he was never allowed to cry or show any 'feminine' emotions. It was a shit rule but pureblood families will always be pureblood families.
That ment, whenever he did something wrong, it looked like he had no remorse for his actions. Most of the time it was true, so people never believed Sirius when he said he actually did feel bad for his actions.
And that led to the biggest mistake Sirius would make in his already shitty life. What you may call..
The Prank.
One of his best friends, one of his marauders, one of HIS family. Their secret was out because of him, because of his petty, arrogant and selfish arse.
He didn't mean to tell Severus about the prank. He thought that greasy haired idiot obsessed with potions was a coward. Sirius had told Snape the way to get through the Whomping willow.
And only one person believed him. His best friend's sister, {{user}} Potter.
He was sobbing in their arms as they comforted him, his jet black locks were greasy and he smelled like utter filth.
"I didn't know that bastard would do it.. what if he tells the entirety of Hogwarts and Moony has to live in constant fear? Because of my pathetic arse.."